Bug#899154: console switching broken on Polaris11 hardware with amdgpu.dc=1

["Richard B. Kreckel" <kreckel@in.terlu.de>]

Package: linux-image-4.16.0-1-amd64
Severity: normal
Version: 4.16.5-1

With current Debian/testing, I cannot switch consoles once I'm in
graphics mode: Pressing Ctrl-Alt-F1 produces some artifacts on a black
screen, mouse pointer still there and movable but that's it. It is
impossible to switch back or to another console; the box must be reset.

This does not happend when booting without amdgpu.dc=1.

This is a regression with respect to linux-image-4.15.0-3-amd64.